Scanning of images for fraud detection, forms drop out, or color recombination to yield a color image requires the production of multiple images for electronic capture. This multiple imaging scanning requires that the lens be capable of passing sufficient light so that the light beam may be attenuated by the beam splitting function and still deliver images of adequate light intensity, or to utilize reduced light intensity beams to yield a single image of a relatively higher light intensity.
Wherever multiple images are required from the scanning station, both high levels of illumination are required at the object as well as very fast lenses which are essential in the scanning system in order to deliver sufficient light density at the image plane of the lens so that the capture device can capture the image for subsequent electronic processing. To maintain the illumination density on the object at a low enough level to prevent burning or scorching while at the same time to use lenses with reasonably attainable numerical creates a tradeoff which must be considered in the design and implementation of the systems. There is constantly a need for a larger effective f-stop for the lens of such a system. The typical approach to this problem has been to increase the illumination level on the object or to increase the numerical aperture of the lens whenever image illumination levels cannot be increased.
Conventional beam splitting techniques use a partially reflective surface in a prism to reflect an image onto a separate image plane while passing the balance of the light either to a second image plane or to an additional beam splitting surface. This conventional beam splitting requires enough light energy to ensure that the image focused on each of several image planes has sufficient light intensity or light density to be captured by a charge coupled device (CCD) positioned at each image plane. Since beam splitting is a subtractive process that requires the light level of the beam entering the beam splitter to be adequate to produce the plural images and to compensate for the light losses of transmission in the beam splitter, the only effective solution is to provide in the incoming beam a high enough light density to accommodate all the subtractive factors and transmission losses. The images produced may be variously filtered for forms dropout, fraud detection, or used for optical character recognition (OCR).
For forms dropout, at least two images of the same object must be simultaneously captured using different filtration as is conventional. These requirements dictate extremely high and correspondingly hot illumination density levels on the documents and/or extremely fast (small f-stop) lenses.
Due to the small numerical aperture of the imaging optics existent within the conventional scanning station, a very substantial amount of radiated illumination and image information escapes the lens, accordingly are unused, and serve only to consume power for illumination without providing any corresponding benefit.